You must be the judge of what 50% and 85% is. You should be able to figure this out after a few rounds. You should be able to maintain the same wattage or RPM each time, so slow down if you're unable to recover enough to maintain your desired pace. We will use a linear progression from week to week.

Time to figure out what you're made of. Are you trying to get better or are you just going through the motions?